The present invention relates to a method of and an apparatus for working a screw rotor incorporated into a screw compressor, and more particular, to a method of and an apparatus for working a screw rotor, in which working of grooves is enabled in high accuracy and in high efficiency, an end mill used therefore, and a method of manufacturing a screw compressor.
In working of grooves of a screw rotor incorporated into a single screw compressor, there is conventionally known a method of setting a work material on a first axis of rotation, setting a tool on a second axis of rotation perpendicular to the first axis of rotation, rotating the two axes in synchronism, and further increasing a turning radius of the tool, minute by minute, set on the second axis of rotation as working proceeds, thereby forming grooves shape of a screw rotor (see, for example, JP-T-6-506640).
However, a finish tool used in JP-T-6-506640 is a formed tool, which is especial in shape in order to prevent interference in other locations than a point of cutting. Also, since a formed tool is used to perform shaving working, cutting resistance at a space bottom becomes large and minute cutting is forced to perform, so that an obstacle is put in shortening of working time and an improvement in tool life.
On the other hand, in order to solve the problems described above, there is separately proposed realization of working of a screw rotor in a general-use facility, in which a commercial five-axis NC machine is used as a base machine, rough working with an end mill tool is heightened in efficiency, and circular movements of two perpendicular axes are added to increase a turning radius of the tool (see, for example, International Publication No. WO2004/089569).
With JP-T-6-506640, however, shaving working with a tool of a specific shape is performed in grooves side finish working out of working of grooves of a screw rotor, so that it is necessary to manufacture a tool of a specific shape in conformity to a product shape. Also, on account of a specific shape, an error is liable to generate in setting of coordinates of a tool cutting edge position, so that there is a need of correction in dummy working and an adjustment jig. Also, on account of shaving working, in which a work material and a tool move in synchronism, the relative speed of the work material and the tool makes a cutting speed to cause a problem that high speed cannot be desired and an increase in working efficiency cannot be achieved.
Also, the working method as in International Publication No. WO2004/089569 involves a problem that an exclusive facility is necessary and a screw rotor cannot be produced due to stoppage of working in a working apparatus.
The invention has been thought of in view of the problems and has its object to provide a method of improving working of grooves of a screw rotor, in particular, working of grooves side in working efficiency, a working apparatus, a working tool, and a method of manufacturing a screw compressor.
A method of working a screw rotor, according to the invention, has a feature in a method of working a screw rotor by controlling at least two axes, that is, rotation of a work and turning of a tool at a time to form a screw tooth space, the method comprising a first step of using a first end mill as the tool to make a predetermined cut in a depth direction of the screw tooth space to perform engraving to a predetermined depth, a second step of using a second end mill, which has a smaller diameter than that of the first end mill, as the tool to perform rough working on a side of the screw tooth space, a third step of using a third end mill, which has a rounded tip end, as the tool to perform rough working on a bottom surface of the screw tooth space, a fourth step of using a fourth end mill, which has a cutting edge portion being shorter than a depth of the screw tooth space in a depth direction and a neck portion being smaller in diameter than the cutting edge portion, as the tool to perform finish working on the side of the screw tooth space, and a fifth step of using a shaving byte, which is shaped in conformity to the bottom surface of the screw tooth space, as the tool to perform finish working on the bottom surface of the screw tooth space.
Also, a method of working a screw rotor, according to the invention, has a feature in a method of working a screw rotor by controlling at least two axes, that is, rotation of a work and turning of a tool at a time to form a screw tooth space, the method comprising a first step of using a first end mill as the tool to make a predetermined cut in a depth direction of the screw tooth space to perform engraving to a predetermined depth, a second step of using a second end mill, which has a smaller diameter than that of the first end mill, as the tool to perform rough working on a side of the screw tooth space, a third step of using a third end mill, which has a rounded tip end, as the tool to perform rough working on a bottom surface of the screw tooth space, a fourth step of using a sixth end mill, which is smaller in diameter than the first end mill, as the tool to perform finish working on the side of the screw tooth space with a cutter pass, in which working is divided into a shorter depth than a depth of the screw tooth space in a depth direction and a tool center is moved so as to contact with both lead at a tip end of the sixth end mill and lead on an outside diameter surface of the work, and a fifth step of using a shaving byte, which is shaped in conformity to the bottom surface of the screw tooth space, as the tool to perform finish working on the bottom surface of the screw tooth space.
Since a rotating tool is used for the finish working of grooves side according to the invention, the number of rotation can be heightened to be equal to that in an ordinary end mill working and it is not necessary to use a shaving byte having a specific shape, so that working is made high in efficiency. Also, since the tool is of rotational symmetry, a cutting edge position becomes easy to measure to heighten the tooth space width in accuracy as compared with a shaving byte of a specific shape. As compared with a shaving byte of a specific shape, there is produced an effect that a tool is simple to work, or the like.